Position plotting apparatus

ABSTRACT

Position-plotting apparatus which may be mounted on and is rotatable with the directional antenna of a radio direction finder. The apparatus includes a mounting bracket which may be secured to the antenna, a chart platform mounted on the bracket for rotation independent of the antenna about an axis coinciding with the rotational axis of the antenna for supporting a chart of a given region, locking shoes for releasably locking the chart platform in a selected position relative to the antenna, and a parallel line overlay overlying the chart platform. The overlay has elongated, parallel straight edges, and is mounted for movement over the chart platform with the straight edges of the overlay being maintained parallel to the directional axis of the antenna, permitting lines paralleling the directional axis of the antenna to be drawn on any part of the chart.

United States Pate Carrutliers 1 POSllTION PLOTTING APPARATUS [76]Inventor: Eben 1-1. Carrutliers, 40 Warren,

Warrenton, Oreg. 97146 [22] Filed: June 22, 1972 [21] Appl. No.: 265,191

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Denis H. McCabeAttorney-John W. Stuart [57] ABSTRACT Position-plotting apparatus whichmay be mounted on and is rotatable with the directional antenna of aradio direction finder. The apparatus includes a mounting bracket whichmay be secured to the antenna, a chart platform mounted on the bracketfor rotation independent of the antenna about an axis coinciding withthe rotational axis of the antenna for supporting a chart of a givenregion, locking shoes for releasably locking the chart platform in aselected position relative to the antenna, and a parallel line overlayoverlying the chart platform. The overlay has elongated, parallelstraight edges, and is mounted for movement over the chart platform withthe straight edges of the overlay being maintained parallel to thedirectional axis of the antenna, permitting lines paralleling thedirectional axis of the antenna to be drawn on any part of the chart.

9 Claims. 4 Drawing Figures 1 POSITION PLO'ITING APPARATUS SUMMARY ANDBACKGROUND OF THE INVENTION This invention relates to position-plottingapparatus for use with radio direction finders having rotatableantennas.

A radio direction finder (RDF) is commonly used in navigation todetermine a crafts position. The RDF is used to determine the direction,or bearing, from which a radio signal from a known source is received atthe craft. Knowing the heading of the craft and the direction to thesource of the signal relative to the crafts heading, the bearing to thesignal source can be deter- I mined. By drawing a straight line 'On' anapplicable chart from the signal source at the bearing determinedestablishes that the craft is at some point along the line. Thisprocedure then is repeated, determining the bearing to another radiosignal source coming from a different direction. The point at which thetwo lines thus plotted on the chart intersect indicates the position ofthe craft at that time.

Such plotting in the past generally has required that hearing readingsfrom the RDF be transferred by protractors and other draftinginstruments to a chart separated from the RDF. This is slow andsometimes errors are committed in the transfer of information.

The importance of quickly knowing the precise location of a craft isoften critical in the case of a boat approaching the entrance of aharbor in fog or at night. The utility of the invention is particularlyappreciated by the pilot of a boat at such times.

Various position-plotting devices coupled to radio direction finders indifferent manners have been proposed in the past. For the most part,however, these have been cumbersome, complex, expensive and not readilyadaptable to existing RDF equipment.

A general object of the invention is to provide novel position-plottingapparatus for use with a radio direction finder having a rotatableantenna, which apparatus is inexpensively constructed, and is simple,rapid, and efficient in operation.

Another object is to provide novel position-plotting apparatus whicheliminates the need to transfer bearing readings from an RDF to chartsseparated from the RDF. By eliminating such transfer steps, the chancesfor error are markedly reduced.

More specifically, the apparatus includes a mounting bracket which maybe secured to the rotatable antenna of an RDF for rotation therewith, achart platform mounted horizontally on the bracket and rotatableindependent of the antenna about an axis coinciding with the rotationalaxis of the antenna, releasable locking means for securing the chartplatform in a selected position relative to the antenna, and a parallelline overlay overlying the chart platform mounted for movement thereoverwith a straight edge on the overlay maintained parallel to thedirectional axis of the antenna. In operation, the directional axis ofthe antenna is directed in a known manner toward a radio signal source,the locking means is released and the chart platform is rotated wherebya chart mounted threreon is properly aligned with the area in which thecraft is traveling, and then the chart platform once again is locked inplace. The overlay is shifted laterally over the chart until itsstraight edge intersects the position of the selected radio signalsource on the chart, and a line paralleling the directional axis of theantenna is drawn through the position of the signal source on the chart.A second signal source then is selected and a similar procedure isfollowed. The intersection of the two lines on the chart is the presentposition of the craft.

DRAWINGS These and other objects and advantages will become more fullyapparent when the following description is read in conjunction with thedrawings, wherein:

FIG. 1 is an exploded perspective view of apparatus according to theinvention and a radio direction finder on which the same may be mounted;

FIG. 2 is a top plan view of the apparatus mounted on the radiodirection finder;

FIG. 3 is a front elevation view of the apparatus an radio directionfinder illustrated in FIG. 2; and

FIG. 4 is a cross-sectional view of an edge of a chart platform in theapparatus, taken generally along the line 4-4 in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Referring first specifically toFIG. 1, at 10 is indicated generally a conventional battery-poweredradio direction finder (RDF) having a base 12 and a directional antenna14 mounted on the base for rotation relative thereto about a verticalaxis indicated generally at 16. When the RDF is properly tuned to aradio station, or source, from which radio signals emanate, the signalsreceived by the RDF will be weakest when the directional axis of theantenna, indicated generally by dashed line 18, is pointing directlytoward the station. This is referred to as the null position. This maybe determined either by an audible signal produced by the RDF or by thereading on a signal level indicator indicated generally at 20.

Apparatus according to the invention is indicated generally at 24. Theapparatus includes the following major component parts as illustrated inthe exploded perspective view of FIG. 1; a mounting frame 28, a slidemount, or guide member, 32, a chart mounting platform 36, and a parallelline overlay 40.

Describing mounting frame 28 in detail, it includes a central, elongatedmounting bracket portion 42 having an inverted U-shaped cross section.It defines an elongated channel 44 along its underside for receivingantenna 14. The mounting frame may be secured to the antenna by thetightening of set screws 46 extending into channel 44 and against thesides of the antenna. With the mounting frame secured in proper positionon the antenna, a vertical bore 50 therein coincides with rotationalaxis 16 of the antenna.

The mounting frame also includes a pair of elongated track portions 52,54 which extend outwardly in opposite directions from bracket portion42, normal to channel 44. Track portions 52, 54 have elongated, axiallyaligned guide slots 56, 58, respectively, extending therealong. With themounting frame properly mounted on the antenna track portions 52, S4 andtheir associated guide slots extend radially outwardly in oppositedirections from bore 50 and antenna axis 16 and are at right angles tothe directional axis of antenna 14 and channel 44.

Guide member 32 includes an elongated, substantially planar centralportion 62 and a pair of support portions 64, 66 projecting upwardlyfrom opposite ends of the central portion. A pair of aligning pins 70,72 are secured to and project upwardly from support portions 64, 66,respectively.

A pair of guide blocks 76, 78 are secured to and project downwardly fromthe underside of central portion 62. Blocks 76, 78 each have such widththat they may be snugly, yet slidably, received in guide slots 56, 58,respectively. Guide blocks 76, 78 are so positioned on the guide memberthat a straight line extending between their respective centers issubstantially normal to a straight line extending between aligning pins70, 72. With blocks 76, 78 received in guide slots 56, 58, the guidemember is mounted for movement in a direction extending normal to thelongitudinal axis of channel 44, and thus normal to the directional axisof the an- '7 tenna, with a line extending between aligning pins 70,

72 being maintained substantially parallel to the directional axis ofthe antenna throughout such movement.

An elongated slot 80 aligned with blocks 76, 78 extends across thecenter of the guide member to provide an opening to bore 50 with theguide member in any of its adjusted positions relative to the mountingframe.

Chart platform 36 is disk-shaped and has a planar upper surface. A pin84 is secured to and projects downwardly from the center of theplatform. Pin 84 is received in bore 50 in the mounting frame, thusmounting the platform for rotation relative to the mounting frame andantenna about an axis coinciding with the rotational axis for theantenna. With the apparatus assembled, pin 84 extends through slot 80 inmember 32.

A circular chart 90, of the geographic region in which the craft istraveling at the time, has a diameter substantially equal to thediameter of chart platform 36, and is mounted on the platform. Such achart should have the positions of at least two known radio signalsources noted thereon, such as are indicated generally at 92, 94.Printed as a part of the chart is the equivalent of a compass rose whichis projected as an azimuth scale at the periphery of the chart, and isindicated generally at 93. The scale is so aligned on the chart that thezero on the scale indicates north. The scale can be shown either in trueor magnetic compass directions as desired. However, since the chart willbe used primarily with magnetic compasses, as will be explained later,the scale generally would show magnetic directions.

The chart is fastened to the chart platform by a flexible annularclamping ring 96 extending about the periphery of the platform. As isbest illustrated in FIG. 4, ring 96 includes a web portion 96a which hasa diameter substantially equal to the outer diameter of the chartplatform, and a pair of vertically spaced flanges 96b, 960 secured toand projecting radially inwardly from web 96a. Flanges 96b, 96c arespaced apart a distance equal to, or slightly less, than the combinedthickness of platform 36 and chart 90 so that they may be clamped overthe top edge of the chart and the underside of the platform asillustrated in FIG. 4 to hold the chart on the platform. Since theclamping ring is flexible, upper flange 96b may be deformed upwardly topermit a chart either to be removed therefrom or inserted thereunder.With such a clamping ring, it is an easy matter to change charts on themounting platform to correspond to the geographical region in which acraft is traveling. v

Overlay 40, as illustrated, is a substantially rigid, transparentplastic sheet which has a plurality of elongated, parallel straightedges, indicated generally at 100, 102, 104, 106. The overlay also has apair of holes 108, adjacent its opposite ends which are disposed along aline extending parallel to the straight edges of the overlay. Holes 108,110 are adapted to receive aligning pins 70, 72, respectively. With theapparatus assembled, overlay 40 rests on support portions 64, 66 of theguide member 32 with aligning pins 70, 72 snugly received in holes 108,110 to maintain alignment of the overlay relative to the guide member.The overlay thus is mounted for movement over the chart platform in adirection normal to the directional axis of the antenna, with theparallel straight edges of the overlay maintained substantially parallelto the directional axis of the antenna. The multiple parallel straightedges provided reduce thedistance which the overlay must be moved toalign one of the edges with a desired point on the chart.

A pair of locking members, or shoes, 114, 116 are pivotally mounted onthe opposite extremities of track portions 52, 54, respectively, by pins118, 120. The locking members have inwardly facing, frictional bearingportions 114a, 116a, gripping portions 114b, 116b adjacent their outeredges, and depending portions 114e, 116a. Pins 118, 120 extend throughdepending portions 114e, 1160, respectively, to mount the lockingmembers, whereby their bearing portions may be shifted into and out ofengagement with diametrically opposed peripheral portions of the chartplatform.

An elongated rigid rod 124 is pivotally connected adjacent one of itsends to locking member 114 in a region below pin 118 and adjacent itsother end to locking member 116 in a region above pin 120. Rod 124 thusoperatively interconnects the locking members in such a manner thatdepressing the gripping portion of one of the locking members to swingthat locking mem ber outwardly and away from the chart platform resultsin concurrent outward swinging of the other locking member, and,conversely, swinging of a locking member toward the chart platformresults in concurrent swinging of the other locking member toward theplatform.

Referring specifically to FIG. 3, an elongated, rigid rod 126 ispivotally connected at one of its ends to portion 114c of locking member114 and at its other end extends slidably through a horizontal bore in alug 130 secured to and depending from track portion 52. A collar 132 issecured. as by a set screw, on rod 126 intermediate its ends, and acompression spring 134 is interposed between lug 130 and collar 132.Spring 134 thus acts to bias locking members 114, 116 into frictionalengagement with the periphery of the chart platform to lock it in aselected position relative to the mounting frame.

Also included in the apparatus is a reference member 138 which isattached, as by screws, to one side of base 12 of the RDF. The referencemember has a reference mark 140 thereon which overlies the periphery ofa chart on the platform. A line extending through the rotational axisfor the antenna and reference mark 140 provides a lubber line for thedevice which may be positioned in the craft to parallel the lubber lineon a compass which would be used in conjunction with the device. Thelubber line generally is positioned to extend along a line parallelingthe longitudinal center line of the craft with which it is used.

The apparatus thus described is operable simply and efficiently toobtain a plot of the position of the craft in which it is used.Initially, a chart of the region traveled is mounted on the chartplatform and the RDF is mounted so that the lubber line extendingthrough the rotational axis of the antenna and reference mark 140parallels the lubber line on a compass which would be positioned in aconvenient position near the RDF. The RDF is tuned to the frequency of aknown radio signal source which is shown on the chart. The antenna isro- .tated until a minimum strength signal is obtained, indicating thatthe directional axis of the antenna is pointing directly at the signalsource. The gripping portion of one of the locking members then isdepressed to swing the locking shoes outwardly and away from the outeredge of the chart platform, thus releasing the platform. The chartplatform is rotated independently of the antenna until the azimuthreading on the chart at reference mark 140 corresponds to the reading onthe compass at that time, and the locking members are released to lockthe platform in position. This positions the chart in true relation tothe geographic area it represents. Overlay 40 then is shifted laterallyuntil one of its parallel edges is aligned with the position of theknown station on the chart to which the RDF is tuned. A straight line isdrawn along the staight edge on the chart through the known station. Asecond radio station then is selected and the same procedure is followedto establish a second line on the chart. Where these two lines intersectindicates the position of the craft at that time.

With such apparatus, a plot of the position of a craft may be determinedquickly and easily without the need for transferring bearing readingsfrom the RDF to charts separated from the RDF. Further, the apparatusmay be operated so quickly and easily that several transmitting stationscan be checked in close order, and each one rechecked.

The apparatus also may be used to determine a compass course over anypart of the chart. This is done by rotating the chart platform andadjusting overlay 40 until one of its straight edges extends along thedesired course on the chart. The chart platform then is locked intoposition andthe slide mount moved until one of its straight edgesintersects the center point of the chart. The compass course then may beread directly from the azimuth scale where the straight edge whichpasses through the center of the chart intersects the scale.

While a preferred embodiment of the invention has been described herein,it should be apparent to those skilled in the art that variations andmodifications may be made without departing from the spirit of theinvention.

It is claimed and desired to secure by Letters Patent:

1. Position-plotting apparatus for use in combination with a radiodirection finder having a directional antenna mounted for rotation aboutan upright axis permitting the directional axis of the antenna to bedirected toward a radio signal source, the apparatus in operativecondition comprising a mounting bracket means for securing said bracketto such antenna for rotation therewith,

a chart platform having a generally planar upper sur face,

means mounting the chart platform on the mounting bracket for rotationindependently of the bracket about an axis coinciding with therotational axis for such antenna, with the upper surface of the platformin a substantially horizontal position,

locking means for releasably locking said chart platform in a selectedposition relative to the mounting bracket whereby the platform isrotatable therewith, a parallel line overlay having at least oneelongated straight edge overlying said chart platform, and

means mounting said overlay on the mounting bracket with the straightedge of the overlay parallel to the directional axis of such antenna andfor movement laterally of said chart platform and antenna in a directionnormal to said straight edge with said straight edge maintained parallelto the directional axis of such antenna throughout movement.

2. The apparatus of claim 1, wherein said locking means comprises a pairof opposed locking shoes, means mounting said shoes on opposite sides ofthe chart platform for movement toward and away from the platform, andbiasing means yieldably biasing said shoes into frictional contacttherewith.

3. The apparatus of claim 2, which further comprises manually operablemeans for moving a shoe away from said platform and connecting meansoperatively interconnecting said shoes for producing movement of theother of said shoes away from the platform concurrently with movement ofsaid first-mentioned shoe away from the platform.

4. The apparatus of claim 1, wherein said means mounting the overlaycomprises an elongated track extending outwardly from the mountingbracket in a direction normal to the directional axis of the antenna,and a guide member mounting said overlay for movement along said track.

5. The apparatus of claim 4, wherein said chart platform is supportedover said track and said guide member comprises support portionssupporting the overlay above the chart platform.

6. The apparatus of claim 1, wherein said overlay has a width greaterthan half the width of the chart platform and includes other elongatedstraight edges disposed parallel to said one edge and spaced laterallytherefrom across the width of said overlay.

7. The apparatus of claim 1, wherein the radio direction finder includesa base on which the antenna is mounted for rotation, and wherein saidapparatus further comprises means for indicating the orientation of thechart platform relative to the base.

8. The apparatus of claim 1, wherein said chart platform is circular andis adapted to support on its upper surface a circular chart havingsubstantially the same diameter as the platform, and which furthercomprises an annular clamp for holding such a chart on the platform,said clamp including an annular web portion having a diametersubstantially equal to the diameter of the chart platform and upper andlower flanges projecting radially inwardly from the web, said flangesbeing spaced from each other a distance substantially equal to thecombined thickness of the peripheral edges of the platform and a chartsupported thereon, said upper flange being flexible upwardly from thechart platform to permit insertion of a chart thereunder.

9. Position-plotting apparatus for use in combination with a radiodirection finder having a directional antenna mounted for rotation aboutan upright axis permitting the directional axis of the antenna to bedirected toward a radio signal source, the apparatus in operativecondition comprising a chart platform having a generally planar uppersurface, means mounting the chart platform on the antenna for rotationindependently of the antenna about an axis coinciding with therotational axis of the antenna, locking means for releasably lockingsaid chart platform in a selected position relative to the antenna, aparallel line overlay having at least one elongated straight edge, and

means mounting said overlay on the antenna with the straight edgeoverlying the chart platform and extending parallel to the directionalaxis of the antenna, said mounting means mounting the overlay formovement laterally of the chart platform and antenna in a directionnormal to the directional axis of the antenna with said straight edgemaintained parallel to the directional axis of the antenna throughoutmovement.

1. Position-plotting apparatus for use in combination with a radiodirection finder having a directional antenna mounted for rotation aboutan upright axis permitting the directional axis of the antenna to bedirected toward a radio signal source, the apparatus in operativecondition comprising a mounting bracket means for securing said bracketto such antenna for rotation therewith, a chart platform having agenerally planar upper surface, means mounting the chart platform on themounting bracket for rotation independently of the bracket about an axiscoinciding with the rotational axis for such antenna, with the uppersurface of the platform in a substantially horizontal position, lockingmeans for releasably locking said chart platform in a selected positionrelative to the mounting bracket whereby the platform is rotatabletherewith, a parallel line overlay having at least one elongatedstraight edge overlying said chart platform, and means mounting saidoverlay on the mounting bracket with the straight edge of the overlayparallel to the directional axis of such antenna and for movementlaterally of said chart platform and antenna in a direction normal tosaid straight edge with said straight edge maintained parallel to thedirectional axis of such antenna throughout movement.
 2. The apparatusof claim 1, wherein said locking means comprises a pair of opposedlocking shoes, means mounting said shoes on opposite sides of the chartplatform for movement toward and away from the platform, and biasingmeans yieldably biasing said shoes into frictional contact therewith. 3.The apparatus of claim 2, which further comprises manually operablemeans for moving a shoe away from said platform and connecting meansoperatively interconnecting said shoes for producing movement of theother of said shoes away from the platform concurrently with movement ofsaid first-mentioned shoe away from the platform.
 4. The apparatus ofclaim 1, wherein said means mounting the overlay comprises an elongatedtrack extending outwardly from the mounting bracket in a directionnormal to the directional axis of the antenna, and a guide membermounting said overlay for movement along saiD track.
 5. The apparatus ofclaim 4, wherein said chart platform is supported over said track andsaid guide member comprises support portions supporting the overlayabove the chart platform.
 6. The apparatus of claim 1, wherein saidoverlay has a width greater than half the width of the chart platformand includes other elongated straight edges disposed parallel to saidone edge and spaced laterally therefrom across the width of saidoverlay.
 7. The apparatus of claim 1, wherein the radio direction finderincludes a base on which the antenna is mounted for rotation, andwherein said apparatus further comprises means for indicating theorientation of the chart platform relative to the base.
 8. The apparatusof claim 1, wherein said chart platform is circular and is adapted tosupport on its upper surface a circular chart having substantially thesame diameter as the platform, and which further comprises an annularclamp for holding such a chart on the platform, said clamp including anannular web portion having a diameter substantially equal to thediameter of the chart platform and upper and lower flanges projectingradially inwardly from the web, said flanges being spaced from eachother a distance substantially equal to the combined thickness of theperipheral edges of the platform and a chart supported thereon, saidupper flange being flexible upwardly from the chart platform to permitinsertion of a chart thereunder.
 9. Position-plotting apparatus for usein combination with a radio direction finder having a directionalantenna mounted for rotation about an upright axis permitting thedirectional axis of the antenna to be directed toward a radio signalsource, the apparatus in operative condition comprising a chart platformhaving a generally planar upper surface, means mounting the chartplatform on the antenna for rotation independently of the antenna aboutan axis coinciding with the rotational axis of the antenna, lockingmeans for releasably locking said chart platform in a selected positionrelative to the antenna, a parallel line overlay having at least oneelongated straight edge, and means mounting said overlay on the antennawith the straight edge overlying the chart platform and extendingparallel to the directional axis of the antenna, said mounting meansmounting the overlay for movement laterally of the chart platform andantenna in a direction normal to the directional axis of the antennawith said straight edge maintained parallel to the directional axis ofthe antenna throughout movement.